Stephen J. Turnbull
 d = {first : first, last, addr1, addr2} 

I'm not a huge fan of this solution. It feels a bit like a hack instead of an intended syntax. Since prefixing characters on strings is already a thing, I lean more towards that solution. It's slightly easier to search (e.g. if the notation was d{literal1, literal2, etc}, one might search for "python d-dict"). However, If the above notation gains favor, perhaps it would be better to allow an empty ':' followed by a comma:

d = {:, first, last, addr1, addr2}

I don't much like the Perlyness of that syntax, but it's similar to using a prefix and it might lead to more explicit empty literals like {:} and {,} for dict and set respectively. I'm pretty sure that notation for empty literals has been discussed and rejected before, so I apologize if this brings up well-trodden ground. I'm pretty neutral on the proposal in general.

It may also be possible to add a constructor to dict like:

d = dict.from_locals('first', 'last', 'addr1', 'addr2')
d['tel'] = '123-456-789'

It might require a bit of stack inspection or some other magic, but it should be possible. It might be difficult for IDEs to recognize and hint and it might also be a blind-spot for re-factoring (if you change the name of a local variable).

On Wed, Jun 10, 2020 at 3:06 AM Stephen J. Turnbull <turnbull.stephen.fw@u.tsukuba.ac.jp> wrote:
Chris Angelico writes:
 > On Wed, Jun 10, 2020 at 1:15 PM Stephen J. Turnbull
 > <turnbull.stephen.fw@u.tsukuba.ac.jp> wrote:
 > >
 > > Executive summary:
 > >
 > > Dicts are unordered, so we can distinguish dict from set by the first
 > > item (no new notation), and after that default identifiers to (name :
 > > in-scope value) items.
 >
 > Be careful with this assumption. Python's dictionaries DO retain
 > order,

Thank you for the reminder!  I did forget that point.

 > even if you can't easily talk about "the fifth element" [1], so
 > anything that imposes requirements on the entry listed
 > syntactically first may have consequences.

No requirements imposed!  If iteration order matters and you want to
take advantage of abbreviation, you might have to write

    d = {first : first, last, addr1, addr2, tel='123-456-789'}

but frequently it would just work naturally:

    d = {first : first, last, addr1, addr2}

Admittedly this distinction may be even more subtle than grit on Tim's
screen, or randomizing the hash seed per process.  And I suspect that
people who want this feature will prefer the d{} notation for
consistency inside the braces.

Steve
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